Method of hydraulic transmission of power



United States Patent F Patented: Oct. 10, 1961 wherein R is an alkyl radical having from 1 to 4 carbon atoms with from 2 to 3 carbon atoms being preferred, and n is an integer from 1- to 6 inclusive, with from 3 to 4 being preferred and the total number of carbon atoms must be at least 10, have the properties which meet the specific characteristic requirements of the present-day hydraulic fluids. The properties of some of these polyoxyalkylene glycol esters of the present invention are set forth in the following table in comparison with SAE 10 The present invention relates to fluid compositions and specification 70-R:

Diethylene Triethylene Tetraethyl- Property Glycol Di- Glycol Dlene Glycol SAE 70-R propionate propionate Dipropionate Reflux Boiling Point 525 F 300 min,

Flash Point 145 F.

700 1,800 max. 4.0 4.0. 0.049- 0005-0050.

Water Tolerance:

At -40 F mass 50 cc.

At 140 F pass pass ass 50 cc. Evaporation loss (percent 1oss). 32 percent." 23 percent 14 percent 80 percent max. Corrosion/loss in mgJsq. cm.:

Copper 0.50 max.

Brass 0.50 max.

Steel 0.20 max.

Aluminum 0.10 max.

Cast Iron.-. 0.20 max.

Tinned Iron 020 max.

more particularly to fluid compositions suitable for use in fluid pressure systems such as hydraulic brakes, shock absorbers, hydraulic jacks, hydraulic elevators, and the like.

It is well known in the art that certain specific characteristics are necessary in fluids which are to be used in such systems, which characteristics must all be present if the liquid is to function satisfactorily according to present-day standards. The individual characteristics may be found to be present in many compounds, but a single class of compounds having all of the characteristics in combination is extremely rare and heretofore thought to be non-existent.

The requirements of a hydraulic fluid composition to be satisfactory are, suitable viscosity, high boiling point, low freezing point, non-corrosiveness, limited swelling action on rubber, a relatively small coeflicient of expansion and physical and chemical stability over a wide temperature variation.

Heretofore, there have been proposed various multicomponent compositions such as a lubricant, a solvent, a modifier and one or more oxidation and corrosion inhibitors. Some of the prior art lubricants contained, for example, castor oil, certain polyalkylene glycols, alcohols, and glycol ricinoleates. 'lypical of such solvents are, for example, butyl alcohol, amyl alcohol, and esters of the glycols. The usual modifiers are, for example, the glycols; the anti-oxidants are compounds such as'the bisphenols and phenyl-alpha-naphthylamine; and the corrosion inhibitors may be borax or the like. These systerns have not been satisfactory in many instances. Therefore, it is an object of the present invention to provide a hydraulic fluid which consists of a single class of compounds as the hydraulic component and which substantially meets the combined requirements of todays hydraulic fluids. Further objects will become apparent from the following specifications and claims.

It has now been found that certain diesters of polyoxyethylene glycols having the formula It is thus apparent that the compounds of the present invention even without added solvents, modifiers, antioxidants or corrosion inhibitors, are capable of meeting the requirements as set forth by the Society of Automotive Engineers for hydraulic fluids.

The hydraulic fluid compositions of the present invention have the additional advantage of having a superior lubricity. This property keeps rubber fittings and hoses in a pliable state, thereby reducing cracking and failure of rubber parts due to loss of flexibility with age.

It is understood that minor amounts of corrosion and oxidation inhibitors may be added to further improve the characteristics of the fluids. Thus, for example, from 0.2 to 1.0 percent of compounds usually employed as corrosion inhibitors may be employed. Some of the more common inhibitors, for example Zinc alkyl, dithiophosphate, phenyl alpha-naphthylarnine, Agerite Resin D and the like, may be added. Well known oxidation inhibitors, such as bisphenol A, the alkylor alkanolamines, and trialkanolamine may be used, but it has generally been found unnecessary to add the latter because of the superior stability and inertness of the polyoxyalkylene glycol esters themselves.

The polyoxyalkylene glycol diesters which may be employed in accordance with the present invention are, for

example, diethylene glycol dibutyrate, triethylene glycol dibutyrate, tetraethylene glycol diacetate, pentaethylene glycol diacetate, pentaethylene glycol dipropionate, hexaethylene glycol diacetate, hexaethylene glycol dipropionate, triethylene glycol divalerate and the like.

We claim:

1. In a method of hydraulic transmission of power for activating pressure operated elements the improvement which comprises employing as the activating fluid a diester having the formula i l R-OO (C H40)n-CR wherein R is an alkyl radical having from 1 to 4 carbon atoms, n is an integer from 1 to 6 and the total number of carbon atoms of the diester compound is at least 10.

References Cited in the file of this patent UNITED STATES PATENTS 2,379,249 Muskat June 26, 1945 2,870,195 Heininger Ian. 20, 1959 2,886,590 Montgomery May 12, 1959 4 FOREIGN PATENTS 505,155 Canada Aug. 17, 1954 OTHER REFERENCES Glavis: Polymeric Additives for Synthetic Ester Lubricants, Ind. & Eng. Chem., vol. 42, No. 12, December 1950, pps. 244 1-45.

McTurk; Synthetic Lubricants, WADC Technical Re- 10 port 53-88 by Wright Air Dev. Center, Wright-Patterson Air Force Base, Ohio. 

1. IN A METHOD OF HYDRAULIC TRANSMISSION OF POWER FOR ACTIVATING PRESSURE OPERATED ELEMENTS THE IMPROVEMENT WHICH COMPRISES EMPLOYING AS THE ACTIVATING FLUID A DIESTER HAVING THE FORMULA 